Method for manufacturing composite material pieces by resin transfer moulding

Abstract

A manufacturing process of a large part of composite materials with a high fiber content (more than 58%) using the resin transfer moulding technique, wherein a fiber pellet (26) is placed in a mould (20) and strongly compressed, whilst the resin is injected at a constant reference flow rate value and while the instantaneous pressure at the mould inlet is lower than a reference pressure value. When this reference pressure value is reached, the injection flow rate is reduced to maintain the pressure at this level, and the compression of the pellet (26) is temporarily reduced. The injection flow rate is then altered to the constant reference flow rate value and the compression is increased, to start another cycle.

What is claimed is: 
     
       1. A process for manufacturing composite material parts by resin transfer moulding in a mould containing a fibre pellet, said process comprising the following steps: a) compressing of the fibre pellet in the mould to obtain a fibre content of more than 58%, and simultaneously injecting resin into the mould through a mould inlet at a constant reference flow rate, while an instantaneous pressure at the mould inlet is lower than a reference pressure value,   b) when this reference pressure value is reached, reducing the injection flow rate of the resin into the mould, so that the instantaneous pressure is maintained at a value that is virtually the same as the reference pressure value,   c) temporarily reducing compression of the fibre pellet in the mould;   d) progressively increasing the injection flow rate of the resin into the mould until the reference flow rate is reached; and   e) returning to step a).   
     
     
       2. The process of claim 1, comprising reducing the reference pressure value when the resin is being injected into the mould, thereby causing an immediate change to step b) when the instantaneous pressure is at least equal to the new reference pressure value. 
     
     
       3. The process of claim 1, comprising constantly creating a flow rate regulation signal from at least a first signal which is representative of a difference between the reference pressure value and the instantaneous pressure at the mould inlet, comparing this flow rate regulation signal to the reference flow rate value and emitting a control signal capable of commanding the resin injection at the constant reference flow rate value, in accordance with step a), when the flow rate regulation signal is at least equal to the reference flow rate value, and further capable of commanding the resin injection at a reduced flow rate which varies with the flow rate regulation signal, in accordance with step b), when the flow rate regulation signal is lower than the reference flow rate value. 
     
     
       4. The process of claim 3, wherein the flow rate regulation signal is also created from a second signal which is representative of a difference between two consecutive first signals. 
     
     
       5. The process of claim 3, wherein the control signal is a speed signal entered into a speed variator connected to an electric motor, which drives an actuator that injects the resin into the mould. 
     
     
       6. The process of claim 5, wherein the flow rate regulation signal is also created from a third signal which is representative of a difference between a maximum permissible pressure and an instantaneous pressure at an outlet of the actuator. 
     
     
       7. The process of claim 5, comprising entering into the speed variator a signal, which is representative of a maximum permissible torque value for the electric motor. 
     
     
       8. The process of claim 3, wherein the flow rate regulation signal is created using fuzzy logic.